The present invention relates to parallel-epipedic packing containers of the type having a tearable opening arrangement.
In the manufacture of packing containers, e.g. those which are used in connection with the distribution of milk and similar products, the packing containers are manufactured such modern high-capacity packing machines in that a web of a packing material consisting e.g. of a plastic-coated carrier layer of paper is converted to a tube by joining the longitudinal edges of the web to one another, whereupon the tube is filled with contents and is divided by repeated flattening and sealing in zones situated at a distance from one another transverse to the longitudinal axis of the tube. In connection with the sealing of the tube the same is subjected to a forming process so that the packing containers obtain a tetrahedral or parallelepipedic shape. In those cases where a parallelepipedic shape is imparted to the packing containers, the packing containers will have two flattened sealing fins located along opposite end walls. The sealing fins extend over the said end walls as well as the triangular double-walled lugs adjoining these which are produced during the forming of the package.
It is known that in connection with the said triangular double-walled lugs and with the sealing fin different types of tearing perforations can be arranged, with the help of which an emptying opening for the package can be created. An example of such a tearing perforation is contained in Swedish Pat. No. 213,171, where the tearing perforation is arranged in such a manner that it is at right angles in relation to the fin and crosses over a part of the triangular lug as well as over the upper end wall. A pouring opening of the type which is described in the aforementioned Swedish patent specification has proved to function well, but it nevertheless gives rise to a few problems which may prove troublesome to the user of the packing container. In the first place, on prying open the tearing perforation the triangular lug which bears the perforation on the one hand has to be raised, while on the other hand it has to be flattened in a plane perpendicularly to the normal plane of the lug. The flattening is achieved by compressing the lug by pressure being applied between the outer converging lateral edges. Secondly, the pouring opening obtained cannot be reclosed in such a manner that the opening area can be substantially reduced so as to prevent e.g. dust and foreign particles from dropping into the packing container. These disadvantages can be overcome by a method and apparatus for a package design and an opening device in accordance with the present invention. In the present invention one of the said sealing fins is substantially broader than the other sealing fin. The broader sealing fin has a narrow sealing zone which extends along the whole length of the fin and is located close to the outer part of the sealing fin, along which the thermoplastic layers of the packing material placed against each other in the sealing fin have been caused to fuse together so as to form a tight and durable sealing joint. The braoder sealing fin has close to its base line, i.e., the connecting line to the said end wall and triangular lugs, a tearing perforation which penetrates through the outer layer of the packing material but not through its inner plastic layer. The tearing perforation is constituted of perforation lines in the packing material which lines are arranged so that on formation of the package they will be located parallel with one another and opposite one another in the sealing fin. The tearing perforation extends from the tip of one triangular lug to a point on the central portion of the end wall, and said broader sealing fin in the area between the sealing zones and the tearing perforation is unsealed.